Current commercial dehydrogenation practices as for example in the conversion of ethyl benzene to styrene, suffer from the disadvantages of low conversions, while higher conversion oxydehydrogenations suffer from poor selectivities. Selectivity is especially important in this particular reaction since the starting materials for producing styrene comprise over 80 percent of its manufacturing costs. Thus there is a continuing search for catalytic materials that are more efficient in minimizing side reactions and improving conversion rates.
A number of catalysts and catalytic systems have been disclosed utilizing various phosphates and pyrophosphates for the conversion of alkyl aromatics to derivatives having side-chain unsaturation. For example U.S. Pat. No. 3,923,916 claims nickel pyrophosphate as a superior catalyst for the oxydehydrogenation of alkyl aromatics. U.S. Pat. No. 3,933,932 and U.S. Pat. No. 3,957,897 disclose the use of lanthanum, rare earth and alkaline earth phosphates, respectively, as oxydehydrogenation catalysts for alkyl aromatics. However catalyst compositions containing arsenic, antimony, bismuth or cadmium phosphates which have demonstrated outstanding activity for the dehydrogenation reaction of the present invention have heretofore not been disclosed. Although U.S. Pat. No. 3,873,633 utilizes a cobalt-bismuth-phosphorus-oxygen composition as a catalyst for the oxydehydrogenation of paraffinic hydrocarbons to monoolefins or diolefins, the use of this type of catalyst for the conversion of alkyl aromatics to unsaturated side-chain derivatives has heretofore not been known.